This invention relates to injection of pressurized materials through a manifold, such as injection molding of plastic melt in a hot runner system. More specifically, this invention relates to an improved injection molding hot runner system in which the rate of melt flow is controlled through the gate during an injection molding cycle.
U.S. Pat. No. 5,556,582 discloses a multi-gate single cavity system in which the rate of melt flow through the individual gates is controlled independently via a control system according to specific target process conditions. This system enables the weld line of the part (the section of the part in which the melt from one gate meets the melt from another gate) to be selectively located. It also enables the shape of the weld line to be altered to form a stronger bond.
The ""582 patent discloses controlling the rate of melt flow with a tapered valve pin at the gate to the mold cavity. It also discloses placing a pressure transducer inside the mold cavity. Placing the pressure transducer inside the mold cavity can result in the pressure transducer sensing pressure spikes which can occur when the valve pin is closed. A pressure spike sensed by the transducer can cause an unintended response from the control system, and result in a less precise control of the melt flow than desired.
The control system disclosed in the ""582 patent uses the variables of valve pin position and cavity pressure to determine what position the valve pin should be in. Thus, the algorithm performed by the control system in the ""582 patent utilizes two variables to control the rate of melt flow into the cavity.
An injection molding apparatus is provided that controls the rate of material flow during an injection cycle away from the gate. The control system uses a variable, such as pressure, to adjust the position of the valve pin which forms an adjustable gap with the melt flow bore away from the gate.
In one embodiment, controlling the flow away from the gate provides more precise control of melt flow by enabling the use of a larger valve pin head with a control surface, and avoiding the effects of a pressure spike at the gate.
In another embodiment, an injection molding apparatus is provided that includes a nozzle having a bore for passing material to a gate of a mold. The nozzle has a first end for communicating with the gate of the mold and a second end for receiving material. The apparatus also includes a valve pin having a surface for forming a gap with a surface of the bore away from the gate, in which the size of said gap is increased when the valve pin is retracted away from the gate and decreased when the valve pin is displaced toward the gate.
In another embodiment, an injection molding apparatus is provided that includes a manifold having a bore for passing material, and a nozzle coupled to the manifold having a bore for passing material to a gate of a mold. The nozzle has a first end for communicating with the gate of the mold and a second end coupled to the manifold for receiving material from the bore of the manifold. The apparatus further includes a valve pin having a surface for forming a gap with a surface of the bore of the manifold. The size of said gap is increased when the valve pin is retracted away from the gate and decreased when the valve pin is displaced toward said gate.
In another embodiment, an injection molding apparatus is provided that includes a manifold having a bore for passing material, and at least one nozzle coupled to the manifold having a bore for passing material to a gate of a mold. The at least one nozzle has a first end for communicating with the gate of the mold and a second end coupled to the manifold for receiving material from the bore in the manifold. The apparatus also includes a valve pin that reciprocates in at least a portion of the bore in the manifold, and a plug mounted in a recess of the manifold opposite a side of the manifold where the nozzle is coupled. The plug has a bore through which a stem of said valve pin passes, the bore of the plug through which the stem passes having a smaller diameter than the valve pin head at the valve pin head""s largest point and the recess of the manifold having a larger diameter than the diameter of the valve pin head at the valve pin head""s largest point, so that said valve pin can be removed from the manifold from a side of the manifold that said recess is formed when said plug is removed from the manifold.
In another embodiment, an injection molding apparatus is provided that includes a manifold having a bore for passing material, and at least one nozzle coupled to the manifold and having a bore for passing material to a gate of a mold. The nozzle includes a first end for communicating with the gate of the mold and a second end for receiving material from the manifold. The apparatus also includes a valve pin that reciprocates in the bore of the manifold and includes a valve pin head having a surface for forming a gap away from the gate with a surface of one of the bore of the at least one nozzle and the bore of the manifold. The valve pin includes a stem, a rear section that increases in diameter from the stem toward the gate, and a front cone-shaped section that decreases in diameter toward the gate to a point.
In another embodiment, an injection molding apparatus is provided that includes a manifold having a bore for passing material, and at least one nozzle coupled to the manifold and having a bore for passing material to a gate of a mold. The nozzle has a first end for communicating with the gate of the mold and a second end for receiving material from the manifold. The apparatus further includes a valve pin that reciprocates in the bore of the manifold and includes a valve pin head having a front cone-shaped surface for shutting off material flow to the gate with a surface of one of the bore of the at least one nozzle and the bore of the manifold. The front cone-shaped surface includes a raised portion that contacts the surface of one of the bore of the at least one nozzle and the bore of the manifold to prevent material flow, and a recessed portion which does not contact a surface of one of the bore of the at least one nozzle and the bore of the manifold when the raised portion contacts that surface.
In another embodiment, a method of injection molding in a system including at least one nozzle coupled to a manifold for delivering material to a gate of a mold is provided that includes the steps of controlling the rate of material flow away from the gate, sensing a single condition related to the rate at which material flows into the gate, and adjusting the rate of material flow to the gate according to a value of the single condition during an injection cycle.